Synthesis, Structures, and Unusual Photoluminescence of O- and N-Functional Cyclohexasilanes

The reaction of chloropermethylcyclohexasilanes Si 6 Me 12 - n Cl n ( n = 1−3) with lithium silanolates affords the siloxy derivatives Si 6 Me 12 - n (OR) n ( n = 1−3; R = SiMe 3, SiMe 2 -t- Bu). All compounds exhibit bathochromically shifted first UV absorption maxima and room-temperature photoluminescence in solution with emission maxima near 340 nm and remarkably enhanced luminescence intensity as compared to the data for Si 6 Me 12 . The solution photoemission spectra of the corresponding aminocyclohexasilanes Si 6 Me 12 - n (NR 2 ) n ( n = 1, 2; R = −SiMe 3 ), which are accessible from Si 6 Me 12 - n Cl n and LiN(SiMe 3 ) 2, do not show any luminescence above 300 nm. Crystal structure analyses of the 1,3- and 1,4-disubstituted derivatives exhibit the cyclohexasilane ring in the chair conformation with the −OR or −NR 2 groups in either axial or equatorial positions, depending on the steric bulk of the hetero substituents.